1. Field of the Invention
The present invention relates to an air turbine handpiece which can be usefully applied to medical treatment or the like.
2. Description of the Related Art
A medical handpiece, preferably a dental handpiece is disclosed in, for example, U.S. Pat. No. 4,020,556. The known handpiece comprises a grip portion and a head portion which is disposed at an tip of the grip portion. A chamber is formed in the head portion. A rotor having a turbine blade portion is rotatably disposed in the chamber. A rotation shaft is attached to the rotor. A cutting tool is detachably attached to the rotation shaft. A supply tube for supplying compressed air to the turbine blade portion is incorporated in the grip portion. Two nozzle tubes are connected to a tip of the supply tube, and tip openings of the two nozzle tubes are opened to the chamber. In the chamber, exhaust openings are formed above and below the tip openings of the two nozzle tubes, and exhaust flow paths extends from the exhaust openings through the grip portion along a direction of its length. The turbine blade portion has a plurality of turbine blades which are arranged in a circumferential direction at intervals. Operating surfaces (the surface to which air is injected from the nozzle tubes) of the turbine blades arcuately extend in the vertical direction. In the handpiece, the compressed air is injected through the supply tube and the nozzle tubes toward the turbine blades of the turbine blade portion, and the turbine blade portion, the rotation shaft, and the cutting tool are rotated in a specified direction by the injected compressed air. The air which is injected to the turbine blades flows in upward and downward directions along the operating surfaces of the blades and is then exhausted to an outside through the exhaust openings which are formed above and below the nozzle tubes.
Another handpiece is disclosed, for example, in U.S. Pat. No. 3,386,702. The handpiece has a rotor which is rotatably disposed in a chamber. A rotation shaft is fixed to the rotor, and a cutting tool is attached to the rotation shaft. The rotor has first and second turbine blade portions which are separately arranged in an axial direction of the rotor. Each of the first and second turbine blade portions has first and second portions which are arranged in the circumferential direction at intervals. Plural stationary guide vanes for guiding air from the first turbine blade portion to the second turbine blade portion are arranged between the first and second turbine blade portions. A nozzle opening is disposed above the first turbine blade portion of the rotor, and an exhaust opening is disposed below the second turbine blade portion. Air injected from the nozzle opening acts on the turbine blade of the first turbine blade portion and flows along the turbine blade portions. The air is then guided by the stationary guide vanes from the first turbine blade portion to the second turbine blade portion to act on the second turbine blade portions of the second turbine blade portion and thereafter exhausted to the outside through the exhaust opening. In this way, air from the nozzle opening acts on the turbine blade portions of the first and second turbine blade portions. Therefore, the rotor is rotated at relatively high rotation torque.
However, these handpieces have the following problems which are to be solved.
First, when a handpiece is used, for example, in dental treatment, a rotor, i.e., a cutting tool is rotated at a very high velocity of about 400,000 rpm. In order to rotate the rotor at such a high velocity, it is important to efficiently inject compressed air from a nozzle tube, i.e., a nozzle opening toward a turbine blade portion. In the above-described prior art handpieces, however, the nozzle tube has a tip opening which is approximately circular, and hence the rotor cannot be sufficiently efficiently rotated. More specifically, when a nozzle tube has a small tip opening, compressed air acts concentrically on turbine blades of a turbine blade portion but it is difficult to rotate a rotor at high torque because an injection quantity of the compressed air is small. By contrast, when a nozzle tube has a large tip opening, the compressed air is injected to a relatively wide area of each turbine blade of the turbine blade portion and the injection quantity of the compressed air is increased. However, also a quantity of waste air which does not substantially contribute to generating the rotation torque is also increased. The waste air may become as a rotation resistance to the rotor.
Second, the operating surface of each turbine blade of the turbine blade portion extends simply in an arcuate form. Therefore, air injected to the operating surfaces of turbine blades flows upward and downward (or downward) along the operating surfaces of the turbine blades but the air flow is not smoothly conducted. Furthermore, a part of the air which flows upward and downward (or downward) from the operating surfaces of the turbine blades functions as a resistance to the rotation of the turbine blades. As a result, the kinetic energy of the air cannot be converted into the rotation energy of the rotor.
Third, particularly in the handpiece disclosed in U.S. Pat. No. 3,386,702, the rotor comprises the first and second turbine blade portions and the stationary guide vanes are disposed between the first and second turbine blade portions, and hence the head portion with the rotor incorporated in it is larger. The nozzle opening is disposed above the first turbine blade portion and driving air is injected from an upper side to an obliquely lower side. This configuration also causes the head portion to be larger. This configuration has a further disadvantage that the energy of the air cannot be sufficiently efficiently converted into the rotation energy of the rotor. When the head portion is large, it is difficult to perform a cutting operation of molars or dental treatment for children.